1. Field of the Invention
The present invention relates to a mode detecting apparatus for a video cassette recorder. More particularly, the present invention relates to a mode detecting apparatus in which the mode can be linearly accurately detected for controlling the operating mode of deck of the video cassette recorder.
2. Description of the Prior Art
In a video cassette recorder, the mode represents the operating state between the circuits and the mechanism, and the mode is classified generally into a play mode, a still mode, a recording mode, a fast forward winding mode, a rewinding mode, etc. According to the kind of modes, the respective components of the circuits and the mechanisms have to be positioned at the predetermined positions, and therefore, the detecting and controlling of the mode are known to be important matters.
FIG. 1 is a schematic view showing a constitution of a conventional deck mechanism. Referring to FIG. 1, when a loading motor 1 is driven, the driving force of loading motor 1 is transmitted through a worm gear 3 to a cam gear 5 to rotate cam gear 5. The rotation force of cam gear 5 is transmitted through a relay plate 11 (having a rack portion 11a on a side surface thereof) and a relay gear 13 (meshed with rack portion 11a of relay plate 11) to a mode driving plate 15. Mode driving plate 15 operates the drive-related components of the video cassette recorder in such a manner that the are operated at the predetermined positions.
FIG. 2 is a schematic view for showing the constitution of the mode driving section for illustrating in more detail the operation of mode driving plate 15. A mode driving plate 15A is a detailed illustration of mode driving plate 15 of FIG. 1. Mode driving plate 15A is provided with a rack portion 15B on an outer peripheral portion thereof, and rack portion 15B is meshed with relay gear 13. Mode driving plate 15A has an elongate form extending across the deck, and various cam portions are disposed on mode driving plate 15A for controlling various components connected to mode driving plate 15A. The reason why mode driving plate 15A has an elongate form is that mode driving plate 15A receives the driving force from loading motor 1 through cam gear 5, relay plate 11 and the relay gear 13 of FIG. 1, thereby controlling various driving components for driving a tape such as a brake opening and closing device, a tension lever, and a review lever.
FIG. 3 is a schematic view for illustrating the position of mode driving plate 15A within the video cassette recorder. As shown in FIG. 3, mode driving plate 15A is generally provided between a main deck 17 and a main circuit board 19.
When the deck part of a video cassette recorder is driven through mode driving plate 15A, the various mode positions can be detected by a mode switch 7 which is connected to cam gear 5. The detected signals are inputted into a microcomputer (hereinafter, referred to as "micom") 9, and then, the signals are fed back to loading motor 1.
FIG. 4A is a schematic view for illustrating the mode detecting principle in mode switch 7. As illustrated in the drawing, mode switch 7 includes a switching disc 7A and a brush supporting member 7B. Switching disc 7A is provided with a plurality of tracks which are divided into the conductive portions and non-conductive portions, while the brush supporting member 7B supports a plurality of brushes 9a, 9b, 9c and 9d which contact with the tracks of switching disc 7A. The number of tracks and the brushes is generally 3 to 5.
FIG. 4B is a plan view of switching disc 7A. Referring to FIG. 4B, a hatched portion 8a is a conductive portion, while a non-hatched portion 8b is a non-conductive portion. On the switching disc 7A shown in the drawing, there are four tracks T1, T2, T3 and T4 which have conductive portions 8a and non-conductive portions 8b. Correspondingly to four tracks T1, T2, T3 and T4, there are provided first, second, third and fourth brushes 9a, 9b, 9c and 9d on the bottom of brush supporting member 7B. These brushes 9a, 9b, 9c and 9d contact with the tracks T1, T2, T3 and T4 at predetermined positions, thereby producing the on and off signals in each of the brushes. The produced signals are sent to the micom (9 of FIG. 1) so as to detect the mode of the video cassette recorder.
In the case where there are four brushes, the four brushes 9a, 9b, 9c and 9d are capable of detecting 2.sup.4 -1=15 modes excluding the off state of all four brushes 9a, 9b, 9c and 9d. For example, when the brushes 9a, 9b, 9c and 9d are contacted with the line A--A of FIG. 4B, the first, third and fourth brushes 9a, 9c and 9d generate "0" signals which are off signals. The second brush 9b generates an "1" signal which is an on signal, and thus, the combined signals "0100" are transmitted to micom 9. Micom 9 compares the received signals with reference signals, thereby discriminating the current deck mode.
In the conventional mode detecting apparatus described above, a rotary type is adopted using various components such as loading motor 1, cam gear 5, switching disc 7A, and a plurality of brushes. Therefore, not only the mechanism is complicated, but also various indirect components such as the switching disc and the brushes are used, with the result that the manufacturing cost is increased. Further, the mode switch is disposed on the cam gear, and therefore, the bulk of the cam gear is increased, and the shape of the cam becomes complicated.
Further, the areas of the conductive portion is different from the peripheral portion to the central portion, and therefore, the conductive contacting areas of the brushes become different, with the result that it becomes difficult to obtain a combined mode signal at the accurate position. Therefore, it may be difficult to detect and to control the deck mode of the video cassette recorder.